You can't take a binary executable and get the original source code (without, of course, having the original source code). The best you can do, as Quzah stated, is use a disassembler (a program that turns binary instructions into assembly) to obtain assembly.

You can take this assembly source file and convert it to C/C++, provided you find a utility to accomplish this. I remember seeing a program that did just that. Do a Google search for "ASM to C". I'm sure it will turn up something.